SrZnSi₃O₈, a synthetic member of the feldspar group

Strontium tecto-zincotrisilicate, SrZnSi₃O₈, is a synthetic member of the feldspar group with monoclinic symmetry (space group P2₁/n, Z = 4). In comparison with the alkali feldspars, the aluminium-richest tetra-hedral site in these minerals is completely substituted by Zn, and the alkali metal M site by strontium. The crystal structure is fully ordered, i.e. there is no mutual co-occupation of the tetra-hedral sites or positional disorder of the M site. Although the tetra-hedral site substituted by Zn exhibits significantly longer bond lengths [(Zn-O) = 1.973 Å] due to the incorporation of the larger cation, there is no noticeable distortion of the SiO₄ tetra-hedra compared to the aluminium-bearing feldspars. The coordination number of Sr²⁺ is [6 + 2], with six short distances to oxygen sites in a narrow range [ = 2.560 Å] and two significantly longer distances > 3.10 Å.